The absorption of radiation in the ultraviolet range by polymeric materials is a major cause of the light-induced degradation therein. It is standard practice to add a low molecular weight UV "stabilizer" to light-sensitive polymers to absorb the light in the destructive range or to quench the energy generated as a result of the excitation of the light-absoring functional groups in the polymer.
Although low molecular weight VU absorbers or quenchers of various types are effective in inhibiting or retarding the destruction of the polymers to which they are added, their extractability in various media and/or their volatility during the processing for fabrication of the polymers at elevated temperatures place a limitation on their utility.
This problem has been remedied to a considerable extent by the synthesis of copolymerizable monomers containing structural moieties capable of functioning as UV absorbers or quenchers. The copolymerization of such monomers results in the formation of copolymers with increased stability, i.e., resistance to degradation upon exposure to UV light, with decreased extractability and volatility. The addition of such polymers to a suitable matrix polymer imparts these properties to the latter. U.S. Pat. No. 4,304,895 discloses the use of 2-hydroxy-4-methacryloyloxybenzophenone and mixtures thereof as a monomeric ultraviolet light absorber copolymerizable with acrylic monomers and useful in the preparation of UV absorbing hard contact lenses.
Similarly, the copolymerization of an allyl-2-hydroxy-benzophenone with an acrylate ester such as methyl methacrylate is described in the U.S. Pat. No. 4,310,650, and the copolymerization of ethylenically unsaturated derivatives of 2,4-dihydroxybenzophenone with other vinyl type comonomers is broadly disclosed in U.S. Pat. No. 3,162,676.
U.S. Pat. No. 3,213,058, to Boyle et al., discloses certain benzotriazole compounds and their incorporation into certain plastics, via reaction with carboxy and hydroxy groups contained in said compounds, as UV absorbers.
U.S. Pat. No. 4,528,311 discloses certain benzotriazole monomers which are copolymerizable with vinyl monomers such as methyl methacrylate to yield optically clear polymers useful in the preparation of intraocular and contact lenses. Representative of the disclosed bezotriazole monomers and a particularly preferred compound is 2-[3'-t-butyl-2'-hydroxy-5'-(3"-methacryloylozypropyl)phenyl]-5-chlorobenz otriazole, which has the structure: ##STR1##
UV absorbing lenses are particularly desirable for use by persons who have had their natural lenses surgically removed owing to cataracts or other deterioration of the lens. The visual correction of aphakia resulting from such lens removal requires the use of high plus corrective lenses, which may be in the form of spectacles, contact lenses, or intraocular lenses.
In the normal eye, a portion of incident light entering the eye is absorbed by various parts of the eye so that only the unabsorbed or transmitted portion strikes the retina. Incident light may comprise the entire spectrum of wavelengths including the ultraviolet, visible, and infrared.
The cornea preferentially absorbs the ultraviolet portion of the light with wavelengths up to about 300 nm (nanometers). The crystalline lens preferentially absorbs ultraviolet light with wavelengths from about 300 up to about 400 nm. In the aphakic eye, where there is no crystalline lens, light having a wavelength higher than 300 nm will be transmitted directly to the retina, and the total spectrum of the light striking the retina in the aphakic eye will be different from that in the normal eye. As a consequence, aphakic patients are very sensitive to light in the ultraviolet range and may experience discomfort or color confusion when exposed to natural light or artificial light having high levels of ultraviolet wavelengths.
Inctrocular lenses and hard contact lenses are presently produced from methyl methacrylate polymers, which exhibit a combination of properties desirable for such products, particularly optical clarity, the capability of being cut and polished to specific optical powers, and chemical inertness.
Modern surgical techniques require an incision of only 2-3 mm for removal of the natural cataractous lens. however, the incision must be enlarged to permit the insertion of the PMMA intraocular lenses in use today. With a larger incision, the possibility of irregular closure and faulty apposition is increased, thereby increasing the possibility of developing astigmatism or other visual aberration as a result of the surgery. One proposed solution to the problem of undesired enlargement of the incision is the use of flexible intraocular lenses that can be inserted in a compressed condition, but which will assume their original shape after fixation in the eye. Silicone polymers possess the necessary flexibility to be used for this purpose, and are therefore being developed for use as intraocular lenses.
This invention provides certain monomers that are compatible with silicone polymers, and which can be incorporated in silicone polymers through covalent bonding to impart ultraviolet light absorbing properties to the silicone polymers containing the monomers.
The silicon containing monomers of the invention are incorporated in silicone polymers through the reaction of olefinic unsaturation in the silicone containing monomer with SiH groups in the silicone polymer. Non-silicon containing monomers containing olefinic unsaturation are capable of reacting in the same way; however, because of enhanced compatibility of the silicon containing monomers with the silicone polymers, compared with compatibility of non-silicon containing monomers with silicone polymers, there is a more complete reaction with the silicone polymer when the monomer contains silicon, which leads to a lower proportion of extractable non-reacted monomer. It is quite desirable for a device designed to be implanted in the living body to have as low an extractable content as possible.